The 3rd Generation Partnership Project, 3GPP, is responsible for the standardization of the Universal Mobile Telecommunication System, UMTS, and Long Term Evolution, LTE. The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network, E-UTRAN. LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative to UMTS. LTE brings significant improvements in capacity and performance over previous radio access technologies. However, while operators' have been successful in providing mobile broadband using LTE deployments, user experience in terms of latency and data rates is a differentiating factor between different operators' networks. The ever increasing end-user demands are a significant challenge to the operators.
The modernization of antenna technologies in practice is moving forward in a high pace, which enables the use of more advanced antenna setups and techniques. Large antenna arrays have been used in radar applications, satellite communications, and point-to-point communications. The possible use of large antenna arrays for wireless cellular communications is also being considered in order to increase capacity and performance in a mobile radio network. The use of multiple antennas combined with adequate processing is one way to improve the spectral efficiency of a communication system.
When using multiple antennas, e.g., in the form of large antenna arrays at base stations in a mobile radio network, transmissions between nodes of the radio network, such as between said base stations and wireless devices, pass over several antenna elements. Therefore, a radio channel between, e.g., a wireless device and a serving base station having a plurality of antenna elements is multi-dimensional in that there is a plurality of propagation paths between the wireless device and the different antenna elements of the serving base station, where each path is associated with a gain and a phase, relative to the other paths or to a reference value. It is important for many reasons to be able to characterize this multi-dimensional channel.
A traditional way of characterizing this type of multi-dimensional channel is by a so-called covariance matrix of the channel, which provides information on a stochastic relationship between signals passing over the different antenna elements. This covariance matrix is often signalled between nodes of the network and also used in signal processing in the communication system, e.g., in beamforming applications.
However, the size of the above-mentioned covariance matrix grows with the square of the number of elements in the antenna array. Large antenna array sizes may hence tax resources concerning computational power and memory storage, even for simple sample covariance estimators. Furthermore, in cases where the channel state information, CSI, that is passed e.g. between nodes in a communication network includes covariance matrix information, the transmission bandwidth of the inter-node link may be overloaded. While this may be manageable for a single link or for moderately-sized arrays, the size of the matrix in combination with a large number of concurrent communication links may become unmanageable.
There is thus a need in the art for improved handling of channel characteristics.